Field of the Invention
The present invention relates to an exhaust gas temperature control apparatus which is disposed in an exhaust pipe passage of an internal combustion engine and controls the temperature of exhaust gas, and to an exhaust gas temperature adjustment apparatus disposed in the exhaust pipe passage.
Description of Related Art
In order to cope with recent regulations on the components of emission gas (exhaust gas) of an internal combustion engine, various types of exhaust gas purification units are disposed in the exhaust pipe passage of the internal combustion engine. These exhaust gas purification units purify the exhaust gas components such as NOx and PM (particulate matter) through chemical reaction between a chemical substance such as catalyst or urea water and the exhaust gas components, and the chemical substance exhibits an optimum purification performance in a certain temperature range. Meanwhile, as a result of the improved combustion efficiency of the internal combustion engine, the temperature of exhaust gas tends to decrease. In view of this, there has been proposed a technique of controlling the bed temperature of a selective reduction catalyst in a subsequent stage to a temperature range in which the NOx purification rate is relatively high. Specifically, a passage containing a heat reservoir and a passage for bypassing the heat reservoir are added to the exhaust pipe passage so as to adjust the temperature of exhaust gas to thereby control the bed temperature of the selective reduction catalyst to the temperature range in which the NOx purification rate is relatively high (see, for example, Patent Document 1).